Just a reef shark

How can I best improve this shot?

Come on man are testing are critique skills or what? you know what to do. Arperature is too small or you made a mistake opening the file in RAW underexposed. If you took it in RAW format up the exposure and see how it looks. If this is out of the camera you need to open up the arperature 2-3 stops and see what effect your strobe will have. The goal is to match ambient light to get a nice blue backgroud and light the shark to give it a little more pop. Arperature 1st seems like the strobe power you have set will be fine. I can see the places where it hit the shark. Composition looks fine, you could have gotten a little closer or zoomed in (if using azoom lens) but it looks fine.

The image is probably underexposed in technical terms and you are losing detail along the bottom of the rear end but this was probably not meant as a fish ID image. The darker tone is moody and fitting for me and the lack of detail in the back draws more attention to the head. The top of the shark appears to be just ambient light and gives a very nice blue metallic smooth look. What I'm trying to figure out is how Alex and some others can make it look like you're in contact with a fish, which gives them more personality. I think eye contact is important and for me this shot is passive (as are most of my own shots). The eye is clearly in focus but I don't have the feeling it is looking at me. Not sure if that is something you control as a photographer or if you have to find a willing subject that happens to show interest in you. Perhaps not the best thing to try with a big shark

Bart

Lighting looks flat to me. Possible ib this case the ambient light was a little flat too, maybe overcast, or deep. I would try to get more from your strobe. Either increase strobe power if you are able to, or open the aperture. May need to increase shutter speed if you want to keep the background exposure the same.